1. Field of the Invention
The present invention relates to an apparatus for measuring a seat weight including a weight of a passenger sitting on an automotive seat and more specifically to a seat weight measuring apparatus capable of simplifying characteristics of load acting on load sensors as much as possible and measuring the seat weight with high precision. The invention also relates to a seat weight measuring apparatus with advantages capable of improving safety when abnormal forces act on the seat or to alleviate strength requirements for the load sensors. The invention further relates to a seat weight measuring apparatus capable of reducing its overall thickness, thereby being constructed in a small size.
2. Description of a Related Art
Automobiles are equipped with seat belts and airbags to secure safety for passengers. In recent years, there is a trend for controlling the operation of such safety devices according to the weight of a passenger for improved performance of seat belts and airbags. For example, the amount of gas introduced into the airbag or an airbag inflating speed and a pre-tension of the seat belt are adjusted according to the weight of a passenger. For that purpose, some means are needed for measuring the weight of a passenger sitting on the seat. An example of such means includes a proposal (Japanese Patent Application No. 9-156666 filed by the applicant of this invention) which involves arranging load sensors (load cells) at four corners under seat rails and summing vertical loads acting on the load cells to determine the seat weight including the weight of a passenger.
The load sensors of the seat weight measuring apparatus described above are preferably of a small type with a measuring capacity of up to some 50 kg. Such load sensors may include: sensors having a strain gauge attached (or formed) on a sensor plate that deflects when it is subjected to a load; piezoelectric sensors; and electrostatic sensors that detect displacements of an elastic member that deflects upon receiving a load.
Meanwhile, Japanese Patent Publication No. JP-A-10-297334 discloses a passenger weight detection apparatus that calculates a gravity center of a loaded seat based on seat weights detected from loads acting on front and rear parts of the seat and which corrects the seat weight according to the calculated gravity center and then, based on the corrected seat weight, estimates the weight of a passenger.
This official gazette, however, was published on Nov. 10, 1998 and was not publicly known at a time when the application (Japanese Patent Application No. 10-121627) that forms a basis for claiming the priority of the present invention was filed on Apr. 16, 1998. Further, the gazette does not disclose a displacement restriction mechanism for the passenger weight detection apparatus that restricts a seat displacement relative to a seat fixing portion within a specified range.
It is an object of the present invention to provide a seat weight measuring apparatus having the following characteristics.
(1) Simplify characteristics of loads acting on the sensors as practically as possible to easily measure the weight of a passenger on the seat.
(2) Improve safety when abnormal force acts on the seat.
(3) Reduce its overall size as well as the machining and assembly costs.
To achieve these objectives, a seat weight measuring apparatus for measuring a seat weight including the weight of a passenger sitting on an automotive seat comprises: seat connecting mechanisms including arms for connecting the seat to seat fixing portions, the arms having a seat side end thereof and a car body side end thereof, one end or both ends pivotally supported on pivots; load sensor mechanisms for receiving and detecting the seat weight applied between the car and the seat; and displacement restriction mechanisms for restricting displacement of the seat relative to the seat fixing portions within a predetermined range the displacement mainly caused by a pivotal motion of the arms.
Because the seat is connected to the car body by the seat connecting mechanisms, which include pivotally supported arms, the displacement of the seat relative to the car body when the seat is loaded is regulated to some extent. Hence, the characteristic of the load acting on the load sensors is simplified, facilitating the measurement of the weight of a passenger on the seat. In this case, it is preferred that the load sensors selectively receive the vertical component of the seat weight bearing on the arms.
An object of what is referred to as the seat weight measuring apparatus in this specification is basically to measure the weight of a passenger on the seat. Therefore, an apparatus that measures only the weight of a passenger by canceling the weight of the seat itself is included in what is called the seat weight measuring apparatus in this specification.
In the present invention, the load sensors preferably receive the seat weight through the arms. In this case, the displacement of the seat can be amplified or de-amplified by the lever action of the arms as it is transmitted to the load sensors. The load range of the load sensors can be changed by a leverage of the arms, making it possible to reduce the size and weight of the load sensors as well as their cost.
Further, it is preferred in the invention that one set of the load sensors be provided on each lateral side of the seat for each of the load sensors to detect a total weight bearing on the whole left or right portion of the seat. This apparatus thus can reduce the number of sensors as well as the number and length of wiring. As an example, the apparatus may employ a construction in which the load sensors each include a sensor plate for receiving a load and a sensor body for detecting a deflection or strain of the sensor plate and in which the sensor plate connects central side ends of the arms of the front and rear seat connecting mechanisms. This construction has the advantage of assembling two sensors into a single sensor and of reducing characteristic variations due to temperature and sensitivity variations.
It is also preferred in the invention that the displacement of the shaft pins of the pivots relative to the car body or seat be restricted by the displacement restriction mechanisms. It is also preferable that the pivot connecting members such as seat brackets and seat rails be provided with means for restricting the deviations of the shaft pins, to reduce the number of constitutional components.
When anchor fixing portions for the seat belts (buckles) are connected to the seat rails or seat, the displacement restriction mechanisms may be provided only to locations near the anchor fixing portions. Alternatively, the displacement restriction mechanisms may be provided to a plurality of locations including those near the anchor fixing portions, and only the displacement restriction mechanisms near the anchor fixing portions may be made robust enough to withstand the tensile force of the seat belts of some 2500 kgf. This allows the overall weight of the seat weight measuring apparatus to be reduced.